June rainfall breaks three-year record

By Greg Ainsworth For the Chronicle

Showers were plentiful across the Gallatin Valley during June, to the delight of anyone trying to develop a green thumb. There haven't been a lot of months with such good news the past couple of years, so let's get right to the numbers.

Preliminary data indicate that 4.0 inches of rain fell at Montana State University's campus station, the highest monthly total in three years. At the airport 3.2 inches were recorded, the most since April 2003. Additional reports include 3.8 inches near Menard in the northern part of the county, and 3.0 inches at the Post Research Farm near Four Corners. The June moisture was particularly welcome after a relatively dry May, when both MSU and the airport were more than an inch below average.

Totals for the three-month "wet season" were right at average for the airport, and a tad above for MSU. Typically, our area receives about 40 percent of its annual precipitation during this April-June period.

As you might expect with the frequent cloudy and showery periods, cool daytime temperatures were the rule during the month. Daily maximum readings were a full four degrees below average at the airport, and three degrees to the cool side at MSU. But the sun peeked through long enough on June 22 to drive the mercury to 92 at the airport, one degree short of the record for the date.

By their very nature, summer thunderstorms are hit-and-miss. Areas right in a storm's path may experience a cloudburst, while it remains dry only a mile or so away. Over the long haul, rainfall from these storms evens out, but in the short term the differences can be significant.

At my house north of Bozeman and east of Springhill Road, one of those thunderstorms produced hail slightly more than 1 inch in diameter early on the evening of June 24. It was quite an interesting sight to watch - and to listen to. I can vouch for the fact that window glass is remarkably strong, by the way. And, you'd be surprised how high a ball of ice can bounce off the grass. Let me know if you observed the same storm -- I'm curious about the extent of the hail.

The National Weather Service classifies a thunderstorm as "severe" if it produces a tornado, or potentially damaging winds (at least 58 mph) or large hail (diameter of at least three-quarters of an inch). So, this was indeed a severe thunderstorm, based on the hail criterion.

Greg Ainsworth of Bozeman has a master's degree in meteorology and keeps an eye on weather and climate issues. He is at ainsworth@theglobal.net

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